This speaker keeps his topic to himself (7)
I believe the answer is:
egotist
This clue could be a double definition.
'this speaker' is the first definition.
The definition and answer can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'his topic to himself' is the second definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'keeps' acts as a link.
Can you help me to learn more?
(Other definitions for egotist that I've seen before include "Self-obsessed person" , "A self-absorbed and conceited person" , "Self-obsessed individual" , "Person with inflated self-image" , "Conceited and self-centred person" .)